Bonding transformers have been employed in the prior art to supply heat energy to coil windings in order to heat them to a temperature level, at which the bonding coat surrounding the wires of the coil windings melts and fuses the windings into an integral mass. Typically, the bonding coat is formed of a thermoplastic or thermoset material. Such material may melt and fuse at a temperature level of approximately 200.degree. C. Accordingly, in order to fuse the coil windings with the required quality, they must be heated as closely as possible to this temperature level. However, because of the variations between coil windings and the variations in the resistance of the wires of the coil windings, if the same amount of heat energy is applied to each coil winding, then some of the windings will be heated to too high or too low of a temperature level. This creates a problem because if the windings are heated to too high of a temperature level, the bonding coat may begin to vaporize and be destroyed instead of fusing. In addition, if a sufficiently high temperature is reached, the insulation layer under the bonding coat may even be detrimentally affected. For example, if the required melting temperature of the bonding coat is approximately 200.degree. C., and too much heat is applied by the bonding transformer so that the temperature of the particular coil winding is raised to 220.degree. C. or 240.degree. C., then the bonding coat and/or insulation layer may be detrimentally affected. On the other hand, if insufficient heat energy is supplied by the bonding transformer to the coil windings, then the bonding coat will not be melted sufficiently to fuse the windings as desired. Accordingly, it can be seen that an accurate control arrangement is required for controlling the amount of heat energy supplied by the bonding transformer to the coil windings so that they are heated to a predetermined temperature level, at which the bonding coat will melt and fuse the windings into an integral mass, independent of the variations between the various windings.
Therefore, it is an object of the present invention to provide a method and apparatus which overcomes the aforesaid problems. Specifically, it is within the contemplation of the present invention to provide an improved method and apparatus for controlling the amount of heat energy supplied by a bonding transformer to coil windings to accurately heat the coil windings to a predetermined temperature level to melt and fuse the windings into an integral mass without detrimentally affecting the bonding coat and/or insulation layer of the coil windings.
It is also an object of the present invention to provide an improved control arrangement for continuously monitoring and sensing the changing current in the bonding transformer as a function of the changing temperature and resistance of the coil winding being heated, while maintaining the voltage in the transformer at a constant level, in order to control the amount of heat energy supplied by the bonding transformer to the coil windings.